The present invention relates to an apparatus for recording/reproducing information using a magnetic recording medium such as a flexible disk, i.e., a floppy disk and, more particularly, to an apparatus for recording/reproducing information by mainly utilizing remanent magnetization perpendicular to a magnetic layer of the recording medium.
Various magnetic recording/reproducing apparatuses are known to record/reproduce information using a magnetic recording medium such as a floppy disk.
In a conventional magnetic recording/reproducing apparatus for recording digital data, when data recorded in the recording medium is updated, i.e., when old data is replaced with new data, the new data is written over the old data. In this case, the old data in the recording medium need not be pre-erased, and new data is recorded at the same position as that of the old data for the following reason.
Digital recording is basically saturation recording. In the conventional apparatus, magnetization is directed along the longitudinal direction, and internal energy is maximum near a magnetization transition point, i.e., a data recording point. Magnetization is most unstable at the transition point. Therefore, the old data does not substantially influence the new data when the new data is written over the old data.
Unlike digital recording, nonmodulated analog recording, normally used in audio or video data recording, is unsaturated recording. Old data must be erased before analog recording is performed.
In a magnetic recording/reproducing apparatus such as a floppy disk used in computers or equipment associated with computers, only apparatuses employing the above-mentioned data overwrite system are in practical use.
A perpendicular magnetic recording system recently developed by Professor Iwasaki at Tohoku University is preferred to perform high-density recording, and further studies are being made for practical applications.
The magnetic recording medium generally used for perpendicular magnetic recording include a particulate medium using barium ferrite and a thin film medium using a thin Co-Cr alloy film. Theory of perpendicular magnetic recording and high-density recording performance obtained therewith have been reported at various meetings and the like, and a detailed description thereof will be omitted. To achieve quality perpendicular magnetic recording problems inherent therein which are unlike those in conventional in-plane magnetic recording systems, i.e., longitudinal magnetic recording systems must be resolved.
The recording problems inherent in perpendicular magnetization have been determined by the present inventor as follows.
FIG. 1 shows the measured data when overwriting is performed in various magnetic recording media using an Mn-Zn ferrite head having an effective gap length of 0.4 .mu.m. For the measurements, the signals were written at a recording density of 10 kBPI, with other signal being then written at a recording density of 20 kBPI, and the OWM (overwrite modulation) represented by an attenuation component of the 10-kBPI signals being plotted. Referring to FIG. 1, the OWM values are plotted along the ordinate, and the current values are plotted along the abscissa.
FIG. 1 shows the characteristic L1 of the first medium, a particulate in-plane orientation medium using Co-.gamma.-Fe.sub.2 O.sub.3 as a magnetic layer material, characteristic L2 of the second medium, a barium ferrite particulate medium of a magnetic layer material, with the perpendicular orientation given by way of a mechanical force, applied upon the coating of the magnetic powder, and characteristic L3 of the third medium, a barium ferrite particulate medium of a magnetic layer material, with perpendicular orientation given by way of a mechanical force and a perpendicular magnetic field of 6 kOe, which are applied when the magnetic powder is coated on a base. The coercive force Hc of the first medium is 600 Oe, and the coercive force Hc of the second and third media is 700 Oe. The thickness of a magnetic layer of each of the first to third magnetic layers is 2 .mu.m.
Referring now to FIG. 1, the overwrite characteristics L2 and L3, with the recording media of magnetization perpendicular to the magnetic layer, surface are degraded as compared with the overwrite characteristics L1 of the in-plane orientation medium. The OWM must generally be designed to be smaller than about -26 to -30 dB. In a head-medium system obtained by the characteristics shown in FIG. 1, an optimal recording current, (a current corresponding to the maximum output) of the input/output characteristics, between 7 and 10 mA 0-p (zero-to-peak). Within this range, the first medium of in-plane orientation has a good overwrite characteristic as is shown by L1. However, the third medium which is oriented more perpendicularly has a poor overwrite characteristic shown as L3. The second medium which is weakly orientated perpendicularly has better overwrite characteistics, shown as L2, than those of the third medium. However, this second medium cannot be utilized practically due to considerations of compatibility between different recording/reproducing apparatuses.
Perpendicular recording is suitable for high-density recording mainly because a demagnetizing field in the medium, and more particularly to a demagnetizing field near a magnetization transition point corresponding to the data recording point is substantially zero, as is well known. This condition indicates that internal energy of the medium is very low and stable. As described above, since the magnetization transition point is unstable in an in-plane recording system, data updating can be performed by an overwrite operation. However, in perpendicular recording, a high amount of energy is required to erase the recorded data. Therefore, the old data (i.e., previously recorded data) cannot be sufficiently erased by an overwrite operation during perpendicular recording.
It is not impossible to improve the overwrite characteristics in perpendicular recording by increasing the gap length of a magnetic recording head or forming a very thin magnetic layer on the medium. However, as perpendicular recording aims at high-density recording, short-wavelength recording is more desirable. In order to perform short-wavelength recording, the gap length of the recording head cannot be increased. In addition, it is very difficult to form a very thin magnetic layer. With a thin film type recording medium, the thickness of the magnetic layer can be decreased, but in this case other characteristics of the media may be effected adversly. The possibility of decreasing the coercive force Hc so as to improve the overwrite characteristics has also been considered. However, when the coercive force Hc is small, both the old and the new data signals deeply permeate the medium, and the final OWM characteristics cannot be significantly improved. As a result, characteristics such as reproduction output and recording density are impaired.